Fluorophosphate glass, which contains P5+ as a cationic component and O2− and F− as anionic components, has low dispersion characteristics and also anomalous partial dispersion characteristics, and hence is known as an optical glass having an excellent chromatic aberration correction function. Examples of such glass are disclosed in Patent Literatures 1 and 2.
Production of an optical element by using the optical glass described in any of Patent Literatures 1 to 3 may involve a step of grinding or polishing the glass. Examples of the production include a case of preparing a lens from a glass material through steps of coarse grinding, fine grinding, polishing, and the like, a case of subjecting a ions prepared by precision press molding to a grinding process called centering, a case of processing a glass material for press molding which is called a preform and which is used for precision press molding, and other cases.
Arsons fluorophosphate glasses, the glass described in Patent Literature 1 is a glass in the region with a high refractive index and a low dispersion, where the fluorine content is relatively low (the F− content is lower than 40 anionic %). This glass has anomalous partial dispersion characteristics and high refractive index characteristics and serves as a lens material which is extremely effective for function improvement and size reduction of optical systems. However, this glass has such a problem that, during a grinding process, the glass is easily broken due to cracks formed in the surface being ground.